Recently, a sound sensing technology is in the spotlight. When using such a sound sensing technology, for example, ambient sound may be detected with a microphone, and based on the detected result, for example, the state of a device, a person, or a pet such as a cat or a dog placed therearound may be detected.
Microphones used in the sound sensing technology require a wide dynamic range and a flat frequency characteristic. In addition, the outputs of the microphones are subjected to a signal processing in a calculation processing circuit such as, for example, a digital signal processor (DSP).
An example of a sound sensing microphone equipped in a personal device such as, for example, a portable phone or a personal computer, or a stationary state monitoring device, is a micro electro mechanical system (MEMS) microphone that employs a semiconductor manufacturing technology. The MEMS microphone in many cases is used by being directly attached to a wiring board.
It is assumed that a microphone is usually used in a state where no object is present therearound. The frequency characteristic of a single microphone is often relatively flat. However, when the microphone is accommodated in a case of a device, the frequency characteristic tends to be changed.
The followings are reference documents.    [Document 1] Japanese Laid-Open Patent Publication No. 2008-167175 and    [Document 2] Japanese Laid-Open Patent Publication No. 8-033084.